A cylinder is a solid having as bases two equal parallel curved surfaces and as its lateral face the continuous surface generated by line connecting the bases and moving along their circum-

The bases are usually circles and such a cylinder is called a circular cylinder, Fig. 77.

A right cylinder, Fig. 78, is one whose side is perpendicular to the bases.

The altitude of a cylinder is the perpendicular distance between the bases.

Fig. 77. Cylinder.

Fig. 78. Right Cylinder.

Fig. 79. Inscribed Cylinder.

A prism whose base is a regular polygon may be inscribed in or circumscribed about a circular cylinder, Fig. 79.